Quantum dot-based environmental indicators

ABSTRACT

A detection method and indicator are disclosed that includes quantum dots that fluoresce under illumination of a first light having a first wavelength to indicate the presence of a predetermined condition, and in particular, a corrosion condition. The quantum dots are surrounded by a shell material that under normal conditions reflect the first light and reacts in the presence of the predetermined condition to permit the first light to illuminate the quantum dot to excite the quantum dot to emit a second light having a second wavelength, which when detected, indicates the presence of the predetermined condition.

FIELD OF DISCLOSURE

This invention relates generally to a method, system, indicator andcoating for the non-destructive detection of a predetermined condition.The invention relates more specifically to a method, system, indicatorand coating that uses quantum dots that fluoresce under illumination toindicate the presence of a predetermined condition, and in particular, acorrosion condition.

BACKGROUND

The early detection of corrosion on metallic structures and vehicles isan extremely time-consuming, costly and difficult task that implicatessignificant economic and safety considerations. For example, aircraft,spacecraft, automotive vehicles, watercraft, and various militaryvehicles operate and/or are exposed to corrosive environments.

For example, military and commercial aircraft undergo routinepre-flight, post-flight and periodic corrosion inspections andcorrective maintenance. Often very expensive and time consumingtechniques, such as x-ray radiography, ultrasonic imaging, andelectromagnetic eddy current inspection methods may be used to detectcorrosion. For many applications, damage due to corrosion is oftendifficult to detect. This is especially problematic on surfaces that aredifficult to access with detection equipment.

In the past, various approaches have been employed and sensors developedto detect corrosion of metallic structures including the use of coatingsapplied to structure surfaces to sense corrosion. One approach that hasbeen attempted to apply coatings intended to act as a sensor reactive tocorrosion. For example, color-change pH indicators have beenincorporated into organic coatings for determining the pH gradientsassociated with corrosion. In another example, fluorescent dyes havebeen applied to microelectronic test vehicles to detect pH changesassociated with corrosion of aluminum or gold metallization under anapplied electrical bias in a humid environment. Other attempts haveincluded the use of fluorescing and color-change dyes that have beenapplied to aluminum after corrosion has begun in order to identify thelocation of the hydrous aluminum oxide corrosion product. More recently,paint has been formulated to include different chemicals that fluoresceupon oxidation or upon complex-action with metal cations formed by thecorrosion process.

Many prior fluorescent and luminescent paints have required that a largeportion of the coating be a visual indicator. Such a large concentrationof the additive may negatively affect the performance of the coating.Moreover, many types of pigments alter the coating color and appearance.Such indicators are typically organic based compositions that maydeteriorate and lose their usefulness over time. The organic indicatorsmay also migrate between coats, so it may not be apparent after time haspassed whether a second layer was satisfactorily applied. In addition,many indicators do not show fluorescence in a color that is easy for thehuman eye to detect, so that the contrast between the coating and theuncoated areas are not readily detected.

However, no method, system or coating has been developed that providesan inexpensive and more comprehensive technique for visually revealinglocations of corrosion, even in difficult to inspect locations.

Therefore, a system, method and coating is needed for improved corrosiondetection. Such a system, method and coating should provide for simple,effective application, reliable overall coating, and simple corrosiondetection.

The foregoing examples and limitations associated therewith are intendedto be illustrative and not exclusive. Other limitations of the relatedart will become apparent to those of skill in the art upon reading ofthe specifications and study of the drawings.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems and methods that are meant to beexemplary and illustrative, not limiting in scope. In variousembodiments, one or more of the problems described above in theBackground have been reduced or eliminated, while other embodiments aredirected to other improvements.

According to one exemplary embodiment, a detection method is disclosedthat includes applying a coating to a substrate, illuminating theapplied coating with a first light having a first predeterminedwavelength and detecting a second light having a second predeterminedwavelength. The coating includes a microsphere comprising a quantum dotand a shell surrounding the quantum dot, and the shell is formed of ashell material that reflects the first light. The quantum dot isselected to emit the second light when illuminated by the first light.The shell material selected to react in the presence of a predeterminedcondition to allow the first light to illuminate the quantum dot.

According to another exemplary embodiment, an indicator is disclosedthat includes a quantum dot configured to emit a second light having asecond wavelength when illuminated by a first light having a firstwavelength, and a shell surrounding the quantum dot. The shell is formedof a material that reflects the first light and reacts in the presenceof a predetermined condition to allow the first light to illuminate thequantum dot.

According to another exemplary embodiment, a sensing system is disclosedthat includes a substrate, a coating disposed upon the substrate, alight illumination source providing a first light having a firstwavelength directed at the substrate, and a light detection device fordetecting a second light having a second wavelength. The coatingcomprises a microsphere comprising a quantum dot and a shell surroundingthe quantum dot. The quantum dot is selected to emit the second lightwhen illuminated by the first light. The shell is formed of a shellmaterial that reflects the first light and reacts in the presence of apredetermined condition to allow the first light to illuminate thequantum dot.

According to yet another exemplary embodiment, an article is disclosedthat includes a substrate and a coating upon the substrate, the coatingincluding a microsphere having a quantum dot and a shell surrounding thequantum dot. The quantum dot is selected to emit a second light having asecond predetermined wavelength when illuminated by a first light havinga first predetermined wavelength. The shell is formed of a shellmaterial that reflects the first light and reacts in the presence of apredetermined condition to allow the first light to illuminate thequantum dot.

One advantage of the present disclosure includes a method, system andcoating for detecting an environmental condition by emission of specificwavelengths of light.

Another advantage of the present disclosure includes a method, systemand coating for detecting a corrosive condition by emission of specificwavelengths of light.

Another advantage of the present disclosure includes a method, systemand coating for indicating corrosion of a substrate by emission ofspecific wavelengths of light.

Another advantage of the present disclosure includes a method, systemand coating that provides for objective, quantitative evidence ofcorrosive conditions allowing for an indication of corrosion at an earlystage, and in particular, before significant corrosion of the substrate.

Another advantage of the present disclosure includes a method, systemand coating that permits a high degree of automation in the corrosioninspection process and related documentation.

Further aspects of the method and apparatus are disclosed herein. Otherfeatures and advantages of the present disclosure will be apparent fromthe following more detailed description of the preferred embodiment,taken in conjunction with the accompanying drawings that illustrate, byway of example, the principles of the disclosed embodiment of thedisclosure. The features, functions, and advantages of the presentdisclosure can be achieved independently in various embodiments of thepresent disclosure or may be combined in yet other embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary microsphere of the present disclosure.

FIG. 2 shows another exemplary microsphere of the present disclosure.

FIG. 3 shows another exemplary microsphere of the present disclosure.

FIG. 4 is an illustration of an exemplary application of the disclosure.

FIG. 5 shows an illustration of an exemplary application of the presentdisclosure.

Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

DETAILED DESCRIPTION

The embodiments disclosed will now be described more fully hereinafterwith reference to the accompanying drawings, in which preferredembodiments of the disclosure are shown. However, one must note thatvarious functions and features may be embodied in many different formsand should not be construed as limited to the embodiments set forthherein; rather, these embodiments are provided so that this disclosurewill be thorough and complete and will fully convey the scope of theinvention to those skilled in the art. All composition percents aregiven as weight percents, unless otherwise specified.

According to disclosed embodiments, the present disclosure includes avisual corrosion indictor including a method, system and coating fornon-destructive visual indication of corrosion for use in environmentsthat are either corrosive in nature and/or potentially corrosive. Thevisual corrosion indicator may be used to indicate the presence of acorrosive condition and/or corrosion of a substrate. The visualcorrosion indicator produces a visual display indicative of the presenceof a corrosive environment or corrosion.

FIG. 1 shows an exemplary microsphere 100 according to the disclosure.As can be seen in FIG. 1, microsphere 100 includes a core 110 includinga plurality of quantum dots (QDs) 120 in an optically clear host matrix130. The core 110 is surrounded by a shell 140. The microsphere 100 hasa generally spherical geometry having a diameter ranging from about 1 μmto about 5 μm. In another exemplary embodiment, the microsphere 100 mayhave at least one QD 120. In another embodiment, the microsphere 100 mayhave other geometries, including but not limited to ellipsoidal, cubic,oval or other shape.

The QDs 120 are nanoparticles formed of a semiconductor material havinga maximum geometric length of between about 1 nm and 50 nm. In anotherembodiment, the maximum geometric length may be between about 2 nm and10 nm. In yet another embodiment, the maximum geometric length may beabout 4 nm. The QDs 120 have “artificial” band gaps that are wider forsmaller particles. The QDs 120 absorb light over a broad spectrum, butemit light over a narrow band of wavelengths with photon energies closeto that of the bandgap. QDs have been previously discussed, for example,in U.S. Pat. No. 6,710,366, issued Mar. 23, 2004, which is incorporatedherein by reference in it's entirety.

The core 110 exposed to light at wavelengths shorter than the emissionwavelength of the QDs 120 will emit light in a narrow wave bandcharacteristic of the imbedded QDs 120.

The matrix 130 is formed of transparent or translucent material. In oneembodiment, the matrix 130 may be a polymer, resin, sol get, or otherorganic or inorganic material.

The shell 140 coats the core 110 and is selected to reflect a firstlight, such as an illumination or interrogation light of a predeterminedfrequency, so that no QD-emitted light can be measured. The shell 140 isalso selected to react in the presence of a predetermined condition toallow the first light to illuminate the quantum dot 120.

In one embodiment, the thickness of the shell 140 is selected to reactwith the predetermined condition at a predetermined rate. In anotherembodiment, the shell material forming the shell 140 is selected toreact with the predetermined condition at a predetermined rate.

In one embodiment, the shell 140 is formed of an organic or inorganicreflective material. In another embodiment, the shell 140 is formed ofan inorganic material. For example, the shell 140 may be formed of ametal or metal alloy. In one embodiment, the shell 140 is formed ofaluminum. In another embodiment, the shell 140 is formed of an aluminumalloy. In yet another embodiment, the shell 140 is formed of a metal ormetal alloy selected to corrode at a predetermined rate underpredetermined environmental conditions. In yet another embodiment, theshell 140 is formed of the same material as the substrate.

In the presence of a corrosive condition or environment, the shell 140can be corroded or otherwise become sufficiently transparent to lightilluminating the microsphere 100. In one embodiment, the shell 140 maybe formed of a material that converts or otherwise forms a non-metalliccompound that is sufficiently transparent at some predetermined amountof corrosion for light to penetrate to the core 110 and for the QDs toemit light that escapes the microsphere 100. In another embodiment, theshell 140 may dissolve, disintegrate or otherwise degrade to becomesufficiently transparent to light illuminating the microsphere 100. Theemitted light may be detected by a spectrally filtered imaging device orsystem as an indication of corrosion. In one embodiment, the amount ofcorrosion is recorded to form a record of the progression of thedetected corrosion.

FIG. 2 shows another embodiment of microsphere 100. In this embodiment,microsphere 100 includes a QD 120 surrounded by an inner shell 123,which is in turn surrounded by shell 140. In another embodiment, theshell 123 may surround one or more QDs 120. For example, the shell 123may surround a plurality of QDs in a matrix 130. The inner shell 123 isdepicted as a single shell layer, however, in another embodiment, theinner shell 123 may be formed of one or more shell layers. The innershell 123 may be formed of an inorganic or organic material. In anotherembodiment, the inner shell 123 may be formed of formed of a materialthat converts or otherwise forms a non-metallic compound that issufficiently transparent at some predetermined amount of corrosion forlight to penetrate to the core 110 and for the QDs to emit light thatescapes the microsphere 100. In another embodiment, the inner shell 123may be formed of an inorganic material. For example, the inner shell 123may be formed of a metal or metal alloy. In one embodiment, the innershell 123 is formed of aluminum. In another embodiment, the inner shell123 is formed of an aluminum alloy. In yet another embodiment, the innershell 123 is formed of a metal or metal alloy selected to corrode at apredetermined rate under predetermined environmental conditions.

FIG. 3 shows yet another embodiment of microsphere 100. In thisexemplary embodiment, microsphere 100 includes a single QD 120surrounded by an inner coating 123, which is in turn surrounded by shell140. The inner coating 123 may be formed of a long-chain molecule. Inone example, the inner coating 123 may be formed of polymer. In yetanother embodiment, the inner coating 123 is formed of a long chainmolecule selected to corrode, oxidize or otherwise degrade at apredetermined rate under predetermined environmental conditions.

FIG. 4 shows a microsphere 100 in a non-corroded state “A” and in acorroded state “B” in a coating layer 400. As can be seen in FIG. 4, amicrosphere 100 having a core 110 and a shell 140 in non-corroded state“A”, when interrogated or illuminated by a first light 410 having apreselected wavelength, reflects the first light 410. In one embodiment,the first light 410 has a first wavelength in the range of about 100 nmto about 3000 nm. In another embodiment, the first light 410 has a firstwavelength in the range of about 300 nm to about 2000 nm. In yet anotherembodiment, the first light 410 has a first wavelength in the range ofabout 300 nm to about 1000 nm. The first light wavelength may be a broadrange or very narrow range. For example, a broad range may be from afirst light source such as the sun. In another example, a narrow rangemay be from a first light source such as a laser. As further shown inFIG. 4, a microsphere 100 having a shell 140 in corroded state “B”, whenilluminated by a first light 410, emits a second light 420 having asecond wavelength, which can be detected and interpreted as evidence ofshell degradation. In one embodiment, the detection of the second lightmay be an indication of an environmental condition corrosive to asubstrate. In one embodiment, the second light 420 may have a wavelengthin the range of about 300 nm to about 5000 nm as determined by thequantum dot properties and environment. In another embodiment, thesecond light 420 may have a wavelength in the range of about 300 nm toabout 3000 nm as determined by the quantum dot properties andenvironment. In one embodiment, the coating layer 400 may be a paint, aprimer, a sealant, a protective coating or other layer that provides forthe quantum dot layer.

In one embodiment, the first light 410 may be provided from a lightsource, including but not limited to sunlight, incandescent lightsource, photodiode, laser or other suitable source of light. In oneembodiment, the second light 420 may be detected by a detection systemsuch as, but not limited to a visual detection by an operator,photodiode, or other imaging or non-imaging light detecting instrument.In one embodiment, the detection system may additionally include aspectral filter or other wavelength selective component.

In one exemplary embodiment, microspheres are fabricated that includeQDs selected to emit red light when illuminated by blue light. In thisembodiment, the microspheres are exposed to a blue light from an intenselight emitting diode (LED) source, and the emitted light is detected byan operator using a spectrally filtered imaging device. In oneembodiment, the spectrally filtered imaging device is filtered glassesthat block most of the light at the illumination wavelength (blue light)but pass red wavelengths emitted by the QDs. The operator would be ableto identify if microspheres have been corroded, since they would beobserved emitting red light. In another embodiment, the operator uses adetector tuned to indicate the presence of a predetermined wavelength oflight.

FIG. 5 shows an exemplary application of a coating layer 500 includingmicrospheres 510 upon a substrate 520. The microspheres 510 may be ofany embodiment of microsphere as discussed above. As shown in FIG. 5,the coating layer 500 is illuminated with a first light 530. The firstlight 530 penetrates the coating layer 500 and illuminates themicrospheres 510. The substrate 520 and coating layer 500 include acorrosion region 540. The microspheres 510 a proximate the corrosionregion emit an emission 550 in response to illumination by the firstlight 530. An operator can detect the emission and determine the extentof the corrosion region 540. In one embodiment, the substrate 520 may bean aluminum skin, for example, of an aircraft structure. In anotherembodiment, the corrosion region 540 has not extended to the substrate520, and only the microspheres 510 in a corrosive region of the coatinglayer 500 are corroded, not the substrate 520.

While this disclosure has discussed in the context of corrosiondetection, QD loaded microspheres may be tailored to indicate otherchemical processes by the selection of the shell material. For example,the dissolution of a microsphere shell may serve as an indicator ofacidity, temperature, humidity, air or water pollution or otherenvironmental conditions.

While exemplary embodiments of the disclosure have been described withreference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe disclosure. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the disclosurewithout departing from the essential scope thereof. Therefore, it isintended that the disclosure not be limited to the particular embodimentdisclosed as the best mode contemplated for carrying out thisdisclosure, but that the disclosure will include all embodiments fallingwithin the scope of the appended claims. It is therefore furtherintended that the following appended claims and claims hereafterintroduced are interpreted to include all such modifications,permutations, additions, and sub-combinations as are within their truespirit and scope.

1. An indicator, comprising: a core comprising one or more quantum dotsthat emit a second light having a second wavelength when illuminated bya first light having a first wavelength; and a shell surrounding thecore; wherein the shell is formed of a shell material that reflects thefirst light and reacts in the presence of a corrosive environment toallow the first light to illuminate the one or more quantum dot therebyexciting the one or more quantum dots to emit the second light havingthe second wavelength.
 2. The indicator of claim 1, further comprisingan inner shell disposed between the shell and the core.
 3. The indicatorof claim 1, further comprising a polymer layer disposed between theshell and the core.
 4. The indicator of claim 1, wherein the shell isformed of a material comprising aluminum.
 5. The indicator of claim 1,wherein the first light has a wavelength between about 100 nm and about3000 nm and the second light has a wavelength between about 300 nm andabout 5000 nm.
 6. An article, comprising: a substrate; and a coatingupon the substrate; wherein the coating comprises a microspherecomprising a core comprising one or more quantum dots and a shellsurrounding the core, and wherein the one or more quantum dots emit asecond light having a second predetermined wavelength when illuminatedby a first light having a first predetermined wavelength, and whereinthe shell is formed of a material that reflects the first light; andwherein the shell is formed of a shell material that reacts in thepresence of a corrosive environment to allow the first light toilluminate the quantum dot.
 7. The article of claim 5, wherein themicrosphere further comprises an inner shell disposed between the shelland the core.
 8. The article of claim 5, wherein the microsphere furthercomprises a polymer layer disposed between the shell and the core. 9.The article of claim 5, wherein the coating further comprises at leastone material selected from the group comprising a paint, a sealant, anda primer.
 10. The article of claim 5, wherein the shell materialcomprises aluminum.
 11. The article of claim 5, wherein the first lighthas a wavelength between about 100 nm and about 3000 nm and the secondlight has a wavelength between about 300 nm and about 5000 nm.